I have the ACT extreme pressure plate with street disc clutch.

One day, the clutch pedal just goes to the floor and stays there when I try to start the car. I check the fluid reservoir and it's empty (was full two days before and I had not driven the car since I checked). I refill and bleed the system out, fluid level is good, no leaks anywhere on the slave, master, or any of the lines in between, no leaks under the dash at the clutch pedal, no more air in the lines, and the pedal still goes straight to the floor and won't come back up.

I think either my slave or master cylinder is bad, but without seeing any leaks and having to just order them both and replace one at a time to see which one is wrong, are there any tests I can do to tell me for sure which one is messing up?

 

You might as well replace both at the same time. If one has gone out allready, the other will follow soon. And I don't like being stranded on the side of the road.